Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/04—Alloys based on a platinum group metal
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0466—Alloys based on noble metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
  • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
  • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
  • C22C32/0021—Matrix based on noble metals, Cu or alloys thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
  • H01T13/39—Selection of materials for electrodes

Definitions

• the present invention relates to a spark plug used for an internal combustion engine. Background technology>
• Patent Document 1 describes a noble metal chip composed mainly of Ir, Rh, and Ni. This is because Ir has a high melting point (2410 ° C) and therefore has good durability against consumption by spark discharge (hereinafter also referred to as spark consumption), while taking advantage of the high temperature of Ir (approximately In order to prevent consumption by oxidation and volatilization at 900 ° C or higher (hereinafter also referred to as oxidation consumption), the oxidation resistance can be improved by adding Rh.
• the discharge is the position of the discharge part with respect to the spark discharge gap after operation.
• Patent Document 1 focuses on Ni as a component that suppresses abnormal wear, and adds Ni to the precious metal chip containing Ir and Rh as the main components, thereby reducing spark wear and I. Abnormal consumption as described above could be suppressed while preventing oxidation consumption of r.
• a noble metal chip composed of Ir, Rh, and Ni as the main components as in Patent Document 1 is used for the discharge part, depending on the use conditions, a granular surface may be formed on the surface of the discharge part. In some cases, perspiration occurred, causing dripping, and the surface of the discharge part peeled off in the form of a film.
• the present inventors set a spark plug having a noble metal tip containing Ir as a main component, 1% by mass of Rh, and 1% by mass of Ni with only a center electrode and a spark plug in a fully open throttle position. The operation was performed at 960 rpm for 1 minute and idling for 30 seconds.
• An object of the present invention is a spark plug in which a discharge portion is formed by a noble metal tip, which suppresses spark consumption, oxidation wear, and abnormal wear of the discharge portion, and suppresses sweating and peeling of a noble metal on the discharge portion surface.
• a spark plug according to claim 1 for solving the above-mentioned problem comprises a center electrode, and a ground electrode arranged so that its side faces the tip of the center electrode, facing the spark discharge gap. At least one of the center electrode and the ground electrode at a position where a discharge portion having a discharge surface is formed by welding a noble metal tip, and the noble metal tip has Ir and Rh as main components. , N i, and at least one of Pt and Pd.
• the content of at least one of Pt and Pd is preferably equal to or more than the content of Ni. If the total content of Pt and Pd is less than the content of Ni, there is a possibility that the above-described sufficient effect of suppressing peeling may not be obtained. Therefore, when the content of at least one of Pt and Pd is equal to or more than the content of Ni, sweating and peeling of the noble metal on the surface of the discharge portion can be effectively suppressed.
• the noble metal tip preferably has a content of at least one of Pt and Pd of 1 to 20% by mass. If the total content of Pt and Pd is less than 1%, a sufficient effect of suppressing the above-mentioned peeling may not be obtained.
• the total content of Pt and Pd exceeds 20% by mass, the melting point of the noble metal tip is reduced, and the spark erosion of the discharge part is reduced, which is not preferable. Therefore, by including at least one of Pt and Pd in the above range in the above range, the separation of the noble metal on the discharge portion surface containing Ir, Rh, and Ni as the main components can be effectively performed. It can be suppressed. Further, in order to prevent perspiration that does not lead to peeling, the content of at least one of Pt and Pd in the noble metal tip is more preferably 4 to 8% by mass.
• the noble metal tip is composed of an Ir-based alloy containing Ir as a main component. Ir-based alloys can be suitably used for the discharge part because of their good durability against spark discharge.
• the content of N 2 in the noble metal tip is preferably in the range of 0.5 to 8% by mass. If the Ni content is less than 0.5% by mass, a sufficient effect of suppressing abnormal consumption may not be obtained. On the other hand, the content of Ni is 8 mass. If the ratio exceeds / 0 , the content of Ni becomes too large, and the spark erosion resistance of the discharge part decreases, and the Ni oxide increases, and the oxidation erosion resistance of the discharge part lowers. Therefore, Ni in the above range is contained By doing so, it is possible to effectively suppress abnormal wear of the discharge part containing Ir and Rh as the main components.
• the content of Rh contained in the noble metal tip is preferably in the range of 0.5 to 40% by mass. If the content of Rh is less than 0.5% by mass, a sufficient effect of suppressing the oxidative consumption of the discharge part may not be obtained. On the other hand, if the content of Rh exceeds 40% by mass, the content of Rh becomes too large, and the melting point of the noble metal tip is reduced, so that the spark erosion of the discharge part cannot be effectively suppressed. is there. Therefore, by including Rh in the above range, it is possible to effectively suppress the oxidative consumption of the discharge part containing Ir.
• the noble metal tips are Sr, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr and
• An oxide (including a composite oxide) of an element selected from H f may be contained. This further effectively suppresses the oxidative consumption of Ir at high temperatures.
• the content of the above oxide may be appropriately set in the range of 0.5 to 3% by mass. If the amount is less than 0.5% by mass, the effect of the oxide to prevent the additive metal element from being oxidized and consumed may not be sufficiently obtained. On the other hand, if the oxide content exceeds 3% by mass, the heat resistance of the discharge part may be impaired.
• a spark plug according to claim 9 for solving the above-mentioned problem comprises: a center electrode; a center electrode-side discharge section formed by welding a center electrode-side noble metal tip to a tip of the center electrode; A ground electrode disposed so as to be opposed to the tip end; and a ground electrode-side discharge unit formed by welding a ground electrode-side noble metal tip to the ground electrode.
• the center electrode-side discharge unit and the ground electrode-side discharge unit Forming a spark discharge gap, wherein the center electrode-side noble metal tip contains I, Rh, and Ni as main components, and further contains at least one of Pt and Pd;
• the electrode-side noble metal tip contains Ir and Rh as main components, and the center electrode-side noble metal tip also has a high Rh content.
• the noble metal chips the center electrode side noble metal tip and the ground electrode side noble metal tip
• Ir and Rh as main components are used for the center electrode side discharge part and the ground electrode side discharge part. contains.
• the center electrode-side noble metal tip and the ground electrode-side noble metal tip contain Ir as a main component, it is possible to improve the spark consumption of the center electrode-side discharge part and the ground electrode-side discharge part. By containing Rh, the oxidation resistance of Ir can be improved.
• the center electrode-side noble metal tip contains Ni and at least one of Pt and Pd.
• Ni As the center electrode-side noble metal tip used for the center electrode-side discharge portion, while suppressing abnormal consumption of the center electrode-side noble metal discharge portion containing Ir and Rh,
• Pt, Pt and Pd By containing at least one of Pt, Pt and Pd, it is also possible to suppress the separation of the noble metal on the surface of the discharge part of the noble metal discharge part on the center electrode side containing Ir, Rh and Ni. Can be.
• the temperature of the ground electrode side discharge part is higher than that of the center electrode side discharge part by protruding into the combustion engine compared to the center electrode side discharge part. Will be higher.
• the ground electrode-side noble metal tip used for the ground electrode-side discharge section has a higher Rh content than the center electrode-side noble metal tip.
• Rh content of the noble metal tip on the center electrode side which is less oxidatively depleted than that of the discharge part on the ground electrode side
• Rh content of the noble metal tip on the ground electrode side the expensive Rh The amount used can be minimized.
• the ground electrode side noble metal tip preferably contains 0.5 to 8% by mass of Ni.
• Ni is less than 0.5 mass ° / 0 , a sufficient effect of suppressing abnormal wear may not be obtained.
• the Ni content exceeds 8% by mass, the Ni content becomes too large, and the spark erosion of the discharge part on the ground electrode side decreases. Or the amount of Ni oxide increases, and the oxidation resistance of the discharge part on the ground electrode side decreases, which is not preferable.
• the ground electrode-side noble metal tip has a content of at least one of Pt and Pd of 1 to 20 mass. It is good to be / 0 . Thereby, it is possible to effectively suppress the separation of the noble metal from the discharge part surface of the discharge part on the ground electrode side containing Ir, Rh, and Ni as main components. If the total content of Pt and Pd is less than 1%, a sufficient effect of suppressing the above-mentioned peeling may not be obtained. On the other hand, if the total content of Pt and Pd exceeds 20% by mass, the melting point of the noble metal tip on the ground electrode side is reduced, and the spark-resistant wear of the discharge part on the ground electrode side is reduced. . Further, in the ground electrode-side noble metal tip, it is more preferable that the content of at least one of Pt and Pd is from: to 8% by mass.
• the ground electrode side noble metal tip contains 5.2 to 41% by mass of Ru. Thereby, the occurrence of peeling of the ground electrode-side discharge portion can be suppressed, and the consumption and deformation of the ground electrode-side discharge portion can be suppressed.
• Ground electrode side Noble metal tip 8 to 20 mass. More preferably, Ru of / 0 is contained.
• FIG. 1 is an overall front sectional view showing one embodiment of the spark plug of the present invention.
• FIG. 2 is a partial cross-sectional view of the spark plug of FIG. 1 and an enlarged cross-sectional view illustrating a main part.
• FIG. 3 is an observation photograph showing a state of a discharge portion on the center electrode side due to peeling.
• 3 is the center electrode, 4 is the ground electrode, 3 1 is the center electrode side discharge section, 3 2 is the ground electrode side discharge section, 3 1 ′ is the center electrode side noble metal tip, 3 2 ′ is the ground electrode side noble metal tip, W,
• W-I is a weld.
• FIG. 1 shows the configuration of the present invention.
• FIG. 2 is a longitudinal sectional view showing an example of a park plug 100
• FIG. 2A is an enlarged view of a spark plug 100 around a discharge portion.
• a spark plug 100 including a resistor which is an example of the present invention, includes a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip 21 protrudes, and a tip formed at the tip. With the center electrode side discharge portion 31 protruding, one end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like, and the other end is bent back to the side.
• a ground electrode 4 and the like are disposed such that the side faces the central electrode-side discharge portion 31 formed on the center electrode 3. Further, the ground electrode 4 is formed with a ground electrode-side discharge portion 32 facing the center electrode-side discharge portion 31.
• the center electrode-side discharge portion 31 has a center electrode-side discharge surface 3 1t.
• a spark discharge gap g is formed in a gap between the ground electrode side discharge portion 32 and the ground electrode side discharge surface 32 t.
• the insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through hole 6 for fitting the center electrode 3 along its own axial direction.
• the metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, and a thread portion 7 for attaching the spark plug 100 to an engine block (not shown) is formed on an outer peripheral surface thereof. I have.
• the terminal 13 is inserted and fixed to one end of the through hole 6, and the center electrode 3 is inserted and fixed to the other end of the through hole 6. Further, an antibody 15 is disposed between the terminal 13 and the center electrode 3 in the through hole 6.
• Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal 13 via conductive glass seal layers 16 and 17, respectively.
• a configuration may be adopted in which one of the center electrode side discharge part 31 and the ground electrode side discharge part 32 opposed thereto is omitted.
• a spark discharge gap g is formed between the two.
• the center electrode side discharge portion 31 is formed by connecting a center electrode side noble metal tip 31 on a disk to a Ni-based heat-resistant alloy such as INC0NEL600, INCONEL601 (a trademark of INCO UK), or the like. Or the tip 3a of the center electrode 3 made of Fe-based heat-resistant alloy
• the welded portion W is formed by laser welding and electron beam welding along the outer peripheral edge of the joining surface, and the welded portion W is fixed.
• the ground electrode-side discharge part 32 is formed on the ground electrode 4 made of a Ni-based heat-resistant alloy such as INCONEL600, INC0NEL601, etc.
• the ground electrode-side discharge part 32 is a center electrode-side discharge part.
• the ground electrode 4 noble metal tip 3 2 ′ is aligned with the ground electrode 4, and a welded portion is formed on the joint surface by, for example, resistance welding, and this is fixed. .
• the spark discharge, oxidation wear, and abnormal wear of the center electrode side noble metal discharge part 31 and the ground electrode side noble metal discharge part 32 are suppressed, and the discharge part surface of the center electrode side noble metal discharge part 31 and the ground electrode side discharge are suppressed.
• the separation of the noble metal on the surface of the discharge part of the part 32 can also be suppressed.
• the center electrode side noble metal tip 31 and the ground electrode side noble metal tip 3 2 ′ are Sr, Y, La, Ce, Pr, Nd, Sm, Eu, Contains oxides (including composite oxides) of elements selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr and Hf May be. Thereby, oxidation consumption can be further effectively suppressed.
• the spark plug 100 has a structure in which the temperature of the center electrode side discharge portion 31 tends to increase.
• a core body 35 having relatively higher thermal conductivity than the electrode base material 36 forming the surface layer is formed.
• the core 35 is formed to draw heat from the central electrode side discharge portion 31 to the central electrode 3 side, and is made of Cu, a Cu alloy, or the like.
• the core 35 is formed only on the center electrode 3 side, but the core may be provided on the ground electrode 4.
• a method for manufacturing the spark plug 100 will be described.
• the center electrode side The noble metal tip 31 and the noble metal tip 32 on the ground electrode side mix noble metal powder as a raw material at an expected ratio and melt this to form an alloy ingot.
• a specific melting method for example, a method such as arc melting or plasma beam melting is employed.
• the ingot may be manufactured by compression-molding a noble metal powder blended with a desired composition and then sintering.
• the alloy is processed into a linear or rod-shaped material by one or more of hot forging, hot rolling and hot drawing, and then cut into a predetermined length in the length direction. Formed.
• the diameter is further reduced by hot rolling with a grooved rolling roll and hot swaging, and finally a wire of 0.8 mm or less is drawn by hot drawing. Process into wire of diameter. Then, the wire is cut to a desired thickness, and the center electrode-side noble metal tip 3 1 ′ and the ground electrode-side noble metal tip
• the center electrode-side noble metal tip 31 and the ground electrode-side noble metal tip 32 were prepared by further preparing a spherical noble metal alloy by a known optimizing method, and using the spherical noble metal alloy as a discharge portion as it is. It may be a flat or cylindrical center electrode-side noble metal tip 31 or a ground electrode-side noble metal tip 32 '. Furthermore, the precious metal powder and the binder, which are the raw materials, are blended in the desired ratio, and a compact is manufactured by press molding such as die press molding, CIP molding, and HIP molding. Then, the molded body is degreased and then sintered to obtain the center electrode-side noble metal tip 311 and the ground electrode-side noble metal tip 3 2.
• the center electrode-side noble metal tip 3 1 is welded to the center electrode 3, and the center electrode 3 to which the center electrode-side noble metal tip 3 1 ′ is welded is inserted into the through-hole 6 of the insulator 2. 1, so that they protrude from the insulator 2.
• a conductive glass seal (a glass seal layer 17 after press-fitting and fixing), a resistor (a resistor 15 after press-fitting and fixing), and conductive glass are provided on the rear end side of the center electrode 3.
• the seal (the glass seal layer 17 is formed after press-fitting and fixing) is inserted in this order, and the terminal 13 is inserted into the rear end of the insulator 2 and press-fitted and fixed by a known method.
• the above-described spark plug 100 of the present invention is attached to the engine block at the screw portion 7 and used as an ignition source for the air-fuel mixture supplied to the combustion chamber.
• a discharge voltage is applied between the center electrode side discharge part 31 and the ground electrode side discharge part 32, and a spark is generated in the spark discharge gap g.
• the spark plug 200 of the second embodiment is different from the spark plug 100 of the first embodiment in that the center electrode side noble metal tip 3 1 ′ and the ground electrode side discharge
• the ground electrode-side noble metal tip 32 constituting 32 is mainly different, and the other parts are almost the same. Therefore, the description will be focused on the parts different from the first embodiment, and the description of the similar parts will be omitted or simplified.
• the center electrode-side discharge portion 31 is formed by, for example, using a Ni-based heat-resistant alloy such as INC0NEL600, INC0NEL601 (trademark of INCO UK), etc. Alternatively, it is superimposed on the end face of the tip 3a of the center electrode 3 made of a Fe-based heat-resistant alloy, and a weld W is formed by laser welding or electron beam welding along the outer peripheral edge of the joint face. It is formed so as to be fixed. Further, for example, when the ground electrode-side discharge portion 32 is formed on the ground electrode 4 made of a Ni-based heat-resistant alloy such as INCONEL600 N INC0NEL601, the ground electrode-side discharge portion 32 becomes the center electrode-side discharge portion. At a position facing 31, the ground electrode-side noble metal tip 3 2 ′ is aligned with the ground electrode 4, and a welded portion W is formed on the joint surface by, for example, resistance welding, and this is fixed to the ground surface. You.
• a Ni-based heat-resistant alloy such as INC0NE
• the center electrode side noble metal tip 3 1 ′ is composed of Ir, R h, and Ni as the main components, such as Ir-1 wt% R h—5 wt% Pt-1 wt% Ni. Contain Further, it is made of an Ir alloy containing Pt and / or Pd. This makes it possible to suppress spark wear, oxidation wear, and abnormal wear of the center electrode side discharge section 31, and also to suppress separation of noble metal on the discharge section surface of the center electrode side discharge section 31.
• the ground electrode-side noble metal tip 32 also has Ir, Rh, and Ni as main components, such as Ir-10 wt% Rh—5 wt ° / 0 Pt-1 wt% Ni. And an Ir alloy further containing at least one of Pt and Pd. This makes it possible to suppress spark wear, oxidation wear, and abnormal wear of the ground electrode-side discharge section 32, and also to suppress the separation of the noble metal from the discharge section surface of the ground electrode-side discharge section 32.
• the Rh content of the ground electrode-side noble metal tip 3 2 ′ is larger than that of the center electrode-side noble metal tip 31.
• the temperature of the ground electrode-side discharge portion 32 becomes higher. Oxidation of Ir of the ground electrode-side discharge portion 32 that occurs can be suppressed.
• the spark plug 300 of the third embodiment is different from the spark plug 100 of the first embodiment and the spark plug 200 of the second embodiment in that
• the noble metal tip 31 and the ground electrode side noble metal tip 32 constituting the ground electrode side discharge part 32 are mainly different, and the other parts are almost the same. Therefore, the description will be focused on the parts different from the first and second embodiments, and the description of the similar parts will be omitted or simplified.
• the center electrode-side discharge portion 31 is made of, for example, a Ni electrode heat-resistant alloy such as DiC0NEL600, INC0NEL601 (trademark of INCO UK), etc. Alternatively, it is superimposed on the end face of the tip 3a of the center electrode 3 made of a Fe-based heat-resistant alloy, and a weld W is formed by laser welding or electron beam welding along the outer peripheral edge of the joint face. It is formed so as to be fixed. Also, for example, When the ground electrode-side discharge part 32 is formed on the ground electrode 4 made of a Ni-based heat-resistant alloy such as INC0NEL600 or INC0NEL601, the ground electrode-side discharge part 32 faces the center electrode-side discharge part 31. In this position, the noble metal tip 32 'on the ground electrode 4 is aligned with the ground electrode 4, and a welded portion is formed on the joint surface by, for example, resistance welding, and this is fixed.
• a Ni electrode heat-resistant alloy such as DiC0NEL600, INC0NEL60
• the center electrode-side noble metal tip 31 ′ is composed of Ir, Rh, and Ni as main components such as Ir_1 wt% Rh—5 wt% Pt-1 wt% Ni. And an Ir alloy containing at least one of Pt and Pd. This makes it possible to suppress spark wear, oxidation wear, and abnormal wear of the center electrode side discharge section 31, and also to suppress separation of noble metal on the discharge section surface of the center electrode side discharge section 31.
• the ground electrode-side noble metal tip 3 2 ′ has Ir, Rh, and Ni as main components, such as Ir-1 wt% Rh_1 1 wt% Ru-1 wt% Ni. And an Ir alloy further containing Ru.
• Ir, Rh, and Ni as main components, such as Ir-1 wt% Rh_1 1 wt% Ru-1 wt% Ni.
• an Ir alloy further containing Ru.
• the Rh content of the ground electrode-side noble metal tip 32 is larger than that of the center electrode-side noble metal tip 31.
• a noble metal tip used for each discharge part of a spark plug was manufactured as follows. In order to form various noble metal chips with different compositions shown in Table 1, the initial elemental components were mixed and mixed in various ratios to obtain various raw material powders. Next This raw material powder was pressure-formed into a 1 OmmX1 OmmX130 mm rectangular parallelepiped. The compact was placed in an arc melting furnace and subjected to arc melting to obtain alloy ingots of various compositions. Further, the alloy was hot forged, hot rolled, and hot swaged at about 1,500 ° C, and then hot drawn to obtain an alloy wire having an outer diameter of 0.6 mm. This was cut in the longitudinal direction to obtain a columnar noble metal tip having a diameter (tip diameter) of 0.6 mm and a thickness of 0.8 mm for each composition.
• the samples 1 7, of the rather than to produce the noble metal tip by the above manufacturing method by I r, Rh, N i, P t, Y 2 0 3 of the raw material powder as shown in Table 1 Ratio Blending and mixing, and further, for example, a binder of PVD is mixed to form a mixture.
• the mixture was pressure-formed into a cylindrical compact having a diameter of 0.6 mm and a thickness of 0.8 mm.
• the molded body is heated at 900 ° C. to 1000 ° C. for 5 hours in a hydrogen atmosphere to remove the binder from the molded body.
• the compact after removing the binder was sintered at 2100 ° C for 1 hour to obtain a noble metal tip.
• the oxidation consumption test of the noble metal tip obtained as described above was performed under the following conditions. That is, the weight of each noble metal chip after holding at a temperature of 1100 ° C for 20 hours in the atmosphere was compared with the weight of the noble metal chip before the test. Then, the weight of the precious metal tip after the test is 90 ° / more than the weight of the precious metal tip before the test. The above items were marked with ⁇ , and those with less than 90% were marked with X. However, all precious metal tips weighed more than 90% of the weight before the test.
• the above-mentioned noble metal tip was welded to the center electrode base material 3a made of INCONEL600 by laser welding as a center electrode-side noble metal tip 31 ', thereby producing a spark plug 100 having the form shown in Figs.
• the ground electrode-side discharge part 32 of the ground electrode 4 made by INC0NEL600 had a chip diameter of 0.9 mm and a thickness of 0.6 mm, and contained 20 masses of Pt. /. Precious metal tip on the ground electrode side that is N 1 32 ' It was constituted by. Then, the durability test of each spark plug 100 obtained as described above was performed under the following conditions.
• these spark plugs 100 were attached to a gasoline engine (six cylinders) with a displacement of 2 OOO cc, and the engine was operated for a total of 50 hours at a throttle fully open condition and an engine speed of 560 rpm.
• the spark gap g of each spark plug 100 was set to 1.1 mm, and a durability test was performed.
• the present invention is not limited to the specific embodiments described above, but can be variously modified embodiments within the scope of the present invention depending on the purpose and application.
• the welded portion W to be welded to the center electrode 3 is provided on the outer peripheral edge of the joint surface as shown in FIG. 2B, but is not limited to this. , May be formed continuously in the radial direction. As a result, the center electrode-side noble metal tip 31 can be more securely welded to the center electrode 3.
• the weld between the ground electrode 4 and the noble metal tip 32 'on the ground electrode side is formed by resistance welding, but after resistance welding, laser welding and electron beam welding are performed along the outer peripheral edge of the joining surface.
• a weld may be formed and fixed, or a weld may be formed by laser welding. Thereby, the ground electrode-side noble metal tip 32 can be welded to the ground electrode 4 more firmly.

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